But structurally, they kind of are the same. They live in the same space. You spin up a Project. Each Tech that is going to have any Activity on that Project has to have a Kickoff Activity. Once they've recorded the Kickoff Activity, they are eligible to be matched with Site Visit Activities.
It sounds like a join table between Projects and Technicians, and each Activity has a classification (Kickoff or Site Visit or anything else), anyway when I look at it that way it makes the answer to your present question easy, because you're just looking up conforming records in the same table where you need to answer the question.
The other approach does work, though, I think - or at least it sounds good enough that in my app I'd try to work through it while I was figuring it out. ;) Get your key Kickoff field onto both Technicians and Projects as 'related Kickoff' and go from there..
EDIT: I'm just an interested observer, by no means an expert - just starting my journey in Quick Base so I enjoy thinking about these kinds of structural questions. I'm hoping somebody with a better grasp on possibilities comes along soon to actually help you!